1. Field of the Invention
This invention relates to a working vehicle having a working implement displaceable relative to the working vehicle by a hydraulic actuator, and a controller for generating a control output signal for controlling a position of the working implement in response to control input signals, with reference to predetermined control characteristics.
2. Description of the Related Art
In a typical construction of a working vehicle with a working implement of the type noted above, the controller receives, as control input signals, a set signal from a setter for setting a target height of the working implement, and a detection signal from a positional detecting sensor for detecting a displacement level of the working implement. In response to the control input signals, the controller generates a control output signal with reference to a table of control characteristics, and outputs the control output signal for driving a hydraulic actuator to maintain the working implement at the target level.
When the working implement deviates from the target level under the influence of some turbulence, for example, a control is carried out to return the working implement to the target level. At this time, the corrective control is carried out based on a starting flow rate table stored as predetermined control characteristics. The control characteristics provided by this starting flow rate table are set to increase the flow rate of pressure oil supplied to the hydraulic actuator with the passage of time from a point of starting the control.
This type of working vehicle is considered here, as one example, to have a boom sprayer acting as the working implement (see FIG. 12).
A large working vehicle may include, as the working implement, a storage tank forming part of the boom sprayer and having a capacity of 1300 liters for storing a liquefied fertilizer, water or the like. It is necessary to raise and lower the storage tank with the hydraulic actuator. During an operation to supply water to the storage tank, for example, the storage tank grows heavier with progress of the water supplying operation. When pressure oil inadvertently leaks from the lift cylinder, the working implement descends beyond a dead zone of a set height. This triggers a control for returning the working implement to a target height.
The control is carried out with reference to the starting flow rate table (control characteristics) as noted above. This starting flow rate table is set to supply a large quantity per unit time. As a result, the boom sprayer acting as the working implement is driven rapidly to return the working implement to the target height. Then, the working implement is moved with acceleration to agitate the water in the storage tank, resulting in an inconvenience of the water supply overflowing a supply opening.
The object of this invention is to provide a working vehicle capable of controlling displacement of a working implement, while avoiding inconveniences due to an excessive displacing speed, particularly in performing a corrective control to place the implement at a target level which may be required as a result of leakage of pressure oil from a lift cylinder or the like.
The above object is fulfilled, according to this invention, by a working vehicle comprising a working implement supported by the working vehicle to be displaceable by a hydraulic actuator, and a controller for generating a control output signal for controlling a position of the working implement in response to a control input signal, with reference to predetermined control characteristics, wherein the control characteristics include at least a first control characteristic and a second control characteristic different from each other, the controller selecting a control characteristic to refer to, according to a type of the control input signal.
This construction provides a plurality of different control characteristics, from which an optimal one may be selected according to a control situation. That is, a flow rate characteristic for supplying pressure oil to the hydraulic actuator may be selected appropriately according to a factor requiring movement of the working implement.
For example, the second control characteristic may have a higher time-dependent rate of increase in a quantity of pressure oil supplied to the hydraulic actuator than the first control characteristic. A difference between a set level and an actual level of the working implement is small in the case of pressure oil leakage. A displacement control of the working implement arising from such a factor may be carried out by controlling a starting flow rate based on the first control characteristic having a low rate of increase in pressure oil supply. Generally, when the operator changes the level of the working implement at will, a large difference exists between a set level and an actual level of the working implement. In such a case, a starting flow rate may be controlled based on the second control characteristic having a high rate of increase in pressure oil supply.
In a preferred embodiment by this invention, the controller refers to the second control characteristic for generating the control output signal when the control input signal results from a variation in a set signal from a setter for setting a target level of the working implement, and refers to the second control characteristic for generating the control output signal when the control input signal results from a variation in a detection signal from a displacement detecting sensor for detecting a displacement of the working implement. In a displacement control of the working implement caused by an operation of the setter, a starting flow rate is controlled based on the second control characteristic having a high rate of increase in pressure oil supply.
That is, for correcting a level of the working implement, a plurality of flow rate control characteristics are made available for selective use with reference to a factor requiring the correction of the level of the working implement. Where a pressure oil leakage from the lift cylinder is the cause, the hydraulic actuator is controlled based on the first control characteristic having a low rate of increase in pressure oil supply, to realize a gentle displacement. On the other hand, where a changing operation of the setter is the cause, the level of the working implement is changed at the operator""s will. The hydraulic actuator is controlled based on the second control characteristic having a high rate of increase in pressure oil supply, to realize a rapid displacement.
In a preferred embodiment of this invention, the setter for setting a target level of the working implement is a position setter for setting a height of the working implement relative to the working vehicle. When the position setter is operated, it often is the case that the working implement is moved to a large extent upward or downward. Thus, the control is based on the starting flow rate characteristic having a high increase rate of pressure oil supply. The control is carried out in agreement with the operational feeling of the operator.
In another preferred embodiment of this invention, the setter for setting a target level of the working implement is an upper limit setter for setting an upper limit position of the working implement relative to the working vehicle, the working implement being forcibly displaced to the upper limit position set by the upper limit setter. When the upper limit position relative to the vehicle body is changed by operating the upper limit setter, the working implement must be raised or lowered to a large extent. In this case, the control is based on the starting flow rate characteristic having a high increase rate of pressure oil supply. A quick control is carried out in agreement with the operational feeling of the operator.
In a further preferred embodiment of this invention, the controller refers to the second control characteristic for generating the control output signal when the control input signal results from a variation in a set signal from a draft setter for setting a reference operational load for the working implement, and refers also to the second control characteristic for generating the control output signal when the control input signal results from a variation in a detection signal from a load detecting sensor for detecting an actual operational load acting on the working implement.
What is known as draft control is a control for maintaining a set operational load acting on the working implement. When an operational load exceeding the set load is received, this state must be terminated promptly to protect the working implement. Whether or not the excessive operational load is caused by an operation of the setter, the working implement is raised or lowered by a control based on the control characteristic (i.e. the second control characteristic) having a high increase rate, to eliminate the overload promptly.
In a further preferred embodiment of this invention, the control characteristics include a first control characteristic having a predetermined time-dependent rate of increase in a quantity of pressure oil supplied to the hydraulic actuator, a second control characteristic having a higher time-dependent rate of increase than the first control characteristic, and a deflection control characteristic set to increase the quantity of pressure oil supplied to the hydraulic actuator with a deviation between a set signal from a setter for setting a target position of the working implement and a detection signal from a position detecting sensor for detecting a position of the working implement, and wherein the controller selects one of the first and second control characteristics according to a type of the control input signal, compares the one of the first and second control characteristics selected with the deviation control characteristic, and generates the control output signal with reference to a value for supplying a smaller quantity of pressure oil to the hydraulic actuator.
This construction gives priority to the deviation control, depending on a control input signal. With the deviation control also, the working implement is displaced quickly and efficiently when the above deviation as an amount of control input is large. When the deviation is small, the working implement is displaced smoothly to avoid overshooting.
Other features and advantages of this invention will be apparent from the following description of the embodiment to be taken with reference to the drawings.